1. Field of the Invention
The present invention relates to a die casting machine using vacuum die casting, that is, die casting in a state with pressure in the cavity reduced.
2. Description of the Related Art
A die casting machine is provided with a pair of dies, a fixed die plate and a movable die plate for holding these dies, a clamping apparatus for clamping the dies, an injection apparatus for injecting molten metal into a cavity formed between the dies, a molten metal supplying apparatus for supplying the molten metal to the injection apparatus, and so on. In such a die casting machine, a die casting is obtained by clamping the dies, supplying molten metal into a sleeve of the injection apparatus, injecting the molten metal into the cavity, and filling the cavity with the molten metal.
One of the causes of uneven quality of die castings is the inclusion of gas in the die castings. That is, molten metal injected into the cavity and filled in the cavity at a high speed and under a high pressure forms a turbulent flow in the sleeve and the cavity. Due to this, gas such as air or vaporized parting agent is mixed into the molten metal.
In order to overcome the above problem, there is known the vacuum casting method for decreasing the inclusion of gas and reducing unevenness of die castings caused by the inclusion.
In a die casting machine using the vacuum casting method, as disclosed for example in U.S. Pat. No. 2,785,448, the inclusion of gas into the molten metal is suppressed by injecting the molten metal into the cavity and filling the cavity with the molten metal in a state with the pressure reduced by a vacuum pump.
In the above die casting machine using vacuum casting, in order to cast a product with a high strength and high quality, it is required to be able to create a higher vacuum in the cavity and maintain the vacuum state.
If the cavity is not made a high vacuum, it is difficult to obtain enough of an effect by the vacuum die casting, because gas becomes included in the casting and distortion or a deformation of the product easily occurs when annealing or otherwise heat treating the product after casting.
In order to cast a product with a higher strength and a higher quality, specifically, it is desired to reduce the pressure in the cavity to several tens of Torr.
Further, from the viewpoint of improving the productivity of a die casting machine, it is required to shorten the time required for evacuation by the vacuum pump as far as possible.
An object of the present invention is to provide a die casting machine using vacuum casting capable of achieving a higher vacuum in the cavity.
According to a first aspect of the present invention, there is provided a die casting machine comprising a movable die and a fixed die, a vacuum pump for reducing pressure in a cavity formed between the dies, and an injection apparatus for injecting and filing molten metal into the cavity at a reduced pressure, at least one of the dies including an evacuation path connected with the vacuum pump and communicated with the cavity, a valve element for opening and shutting the evacuation path, and an electromagnetic driving means for making the valve element move linearly in the opening and shutting direction by electromagnetic force.
In the first aspect according the present invention, since an electromagnetic driving means is used for driving the valve element for opening and shutting the evacuation path formed in the die, it becomes possible to rapidly move the valve element.
Further, in the first aspect of the present invention, the valve element may be arranged between the parting faces and form a valve seat portion integrally with a die. Due to this, it becomes possible to reliably open and shut the evacuation path.
According to a second aspect of the present invention, there is provided a die casting machine comprising a movable die and a fixed die, a vacuum pump for reducing pressure in a cavity formed between the dies, an injection apparatus for injecting and filing molten metal into the cavity with a reduced pressure, an ejecting pin, for ejecting a product formed in the cavity, inserted into an insertion hole formed in a die and communicated with the cavity, a sealing member for sealing between the ejecting pin and the insertion hole to prevent air from flowing into the reduced pressure cavity, and a temperature rise prevention means for preventing a rise in the temperature of the ejecting pin due to contact with the formed product.
In the second aspect according the present invention, the temperature rise prevention means is provided to prevent a sealing member such as an O-ring from being damaged by heat.
Due to this, it becomes possible to keep the cavity sealed reliably by the sealing member and prevent air from flowing in and to create a high vacuum in the cavity.
According to a third aspect of the present invention, there is provided a die casting machine comprising a movable die and a fixed die, a vacuum pump for reducing pressure in a cavity formed between the dies, and an injection apparatus for injecting and filing molten metal into the cavity with a reduced pressure, at least one of the dies including an evacuation path connected with the vacuum pump and communicated with the cavity, a plurality of valve elements for opening and shutting the evacuation path, a plurality of electromagnetic driving means for moving the valve elements linearly in the opening and shutting direction by electromagnetic force, and a control means for independently controlling the drive operations of the electromagnetic means.
In the third aspect according the present invention, by independently controlling a plurality of electromagnetic means, it becomes possible to shorten the time required to create a high vacuum in the cavity.